Blind fastener with shear washer

Abstract

A blind fastener wherein a push-pull type setting tool is employed for pulling a stem into a predetermined position relative to a sleeve, and a two element shear washer is provided to fail at a predetermined shear load as created by the compressive load on the sleeve and the reaction tensile pull on the stem. Failure of the shear washer drives a locking collar between the stem and sleeve. The shear washer comprises a pair of concentric but axially offset elements joined together by an annular shear web which, upon shear failure allows one of the elements to drive an annular locking collar between the stem and sleeve. Such shear washer together with the rivet sleeve are serially placed under compression to counteract the tensile force applied to the stem. A further control feature consists of mating surfaces on the stem and sleeve which are caused to be engaged when the relative positions of the stem and the sleeve are proper for locking the rivet, such mating surfaces engaging at that time to cause the force on said washer to exceed the maximum shear strength of the web.

I claim: 
     
       1. A blind fastener for fastening together at least two members comprising in combination, a sleeve adapted for insertion in aligned holes in said members and having a through opening and an enlarged head incapable of passing through said holes,   a stem slidable within said through opening of said sleeve and having an enlarged end portion at the end of said sleeve opposite said head,   a one-piece washer slidably received upon the stem and including a radially outer element of such size as to be engagable with the head of said sleeve and a radially inner element axially offset from said radially outer element in a direction away from said head and being joined thereto by a breakaway portion, said washer adapted to exert force on said head as a unitary structure with said breakaway portion adapted to fracture in response to a predetermined maximum force to separate the two elements,   and a locking member initially separate from both elements of said washer and from said sleeve underlying the radially inner element and being engagable by said radially inner element as a result of and upon said breakaway portion responding to said maximum force to be forced by said radially inner element into cooperating means on said stem and sleeve to lock said stem and sleeve in their relative positions.   
     
     
       2. A blind fastener according to claim 1 wherein said stem is adapted to be gripped by a push-pull blind fastener setting tool to receive a tensile force as a reaction to a compressive force applied to said washer. 
     
     
       3. A blind fastener according to claim 2 wherein said breakaway portion defines the maximum force to be applied to said stem and sleeve. 
     
     
       4. A blind fastener according to claim 3 wherein said washer elements are concentric and are adapted to be forced to substantially coplanar concentric relation upon said tool overcoming said breakaway portion. 
     
     
       5. A blind fastener according to claim 4 wherein said breakaway portion is a shear portion whereby said maximum force is determined by the shear strength of said portion. 
     
     
       6. A blind fastener according to claim 5 wherein said cooperating means on said sleeve and stem comprise cooperating surfaces defining a cavity, and said locking member is a collar to be driven into said cavity by one of said elements when but only when said shear portion of said washer has been overcome. 
     
     
       7. A blind fastener according to claim 6 which further includes engagable surfaces on said stem and sleeve for defining the relative position thereof when said maximum force is applied to said washer and said collar is driven into said cavity. 
     
     
       8. A blind fastener according to claim 7 wherein said collar is annular in shape and is positioned about said stem to be driven by said radially inner washer element upon overcoming the shear portion thereof.